NEXT Christmas? 2011? Whatever happened to Christmas 2010?
The only scheduled flights from Manchester to Fuerteventura are with Monarch. It's too early to book for December 2011 but around Christmas this year they're only offering an outbound flight on Wednesday 22nd December. You could return a week later on Wednesday 29 December or (for a higher fare) on Saturday 01 January. The total return fare for 2 adults and one child (including taxes & charges) , coming back on the 29th, is £896.10. If you come back on 01 January the inclusive return fare rises to £1016.10.
I would think it likely that you could find accommodation (and pay for your transfers) with the remainder of your budget, so your plan seems to be reasonable. (If you need help researching accommodation.please post again. But if you really mean 2011 it's too early to book at the moment).
easyJet operate from Liverpool to Fuerteventura. They also only offer 22 December outbound, with a choice of 29 December or 01 January for the return flight. The inclusive return fare, coming back on the Wednesday is £842.94. Coming back on the Saturday would take the fare up to £917.94.
Ryanair also have a service from Liverpool. Their only availability around Christmas is out on Wednesday 22 December and back on Wednesday 29 December. That's by far the cheapest option at £620.34.
Those prices will give you an indication of what you might have to pay for flights but, if you're really travelling in 2011, it's far too early to actually book anything.
Chris